Component for a hot dip coating system and method for the production thereof

ABSTRACT

A component for a hot dip coating system, which comes into direct contact with an immersion bath of liquid metal during operation of the hot dip coating system, having a metallic base body, wherein at least one portion of a surface of the base body is provided with a three-layered coating, which includes a corrosion-resistant bonding layer arranged directly on the surface portion, a barrier layer arranged on the bonding layer, and a ceramic surface layer arranged on the barrier layer.

The invention pertains to a component for a hot-dip coating system, which component comes into direct contact with an immersion bath containing molten metal during operation of the hot-dip coating system, and which comprises a metallic base body.

The invention also pertains to a method for the production of a component, especially a guide or deflection roller or stabilizing roller (rollers) for a hot-dip coating system, which component comes into direct contact with an immersion bath containing molten metal during operation of the hot-dip coating system.

Various methods for coating a metallic workpiece such as a strip of metal with a metallic coating are known in the steel industry. One of these coating methods is hot dipping, in which a workpiece consisting of a metal which melts at a relatively high temperature or an alloy which melts at a relatively high temperature is completely immersed in a molten immersion bath containing a metal which melts at a relatively low temperature or an alloy which melts at a relatively low temperature. When the workpiece is removed from the molten immersion bath, the liquid metal or the liquid alloy from the immersion bath adheres to the workpiece and forms a solid metallic coating after it has cooled.

Hot dipping is used to aluminize and to galvanize workpieces, for example, processes which are also known as aluminum dip coating and zinc dip coating. A strip-shaped workpiece is pulled through a vessel containing an immersion bath, wherein the immersion bath contains aluminum or zinc in molten form. The strip-shaped workpiece is guided by rollers; at least one of these rollers, such as a deflection roller, is completely immersed in the bath. A roller of this type for guiding a strip-shaped workpiece through an immersion bath is therefore subjected to severe thermal loads and to corrosion stress during the operation of a hot-dip coating system.

To make a roller of this type for a hot-dip coating system more resistant and longer-lasting, it is known from JP H06 228 724 A, for example, that the roller portion of a roller base body, which also comprises two axial bearing journals connected to the roller portion and arranged coaxially to it, can be provided with a coating. Similar ideas are described in EP 0 245 862 A1, EP 0 927 774 A1, EP 2 743 367 A1, and EP 2 145 845 A1, for example.

One of the goals of the invention is to increase the service life of a component for a hot-dip coating system, which component comes into direct contact with an immersion bath containing molten metal during operation of the hot dip coating system.

This goal is achieved by the independent claims. Advantageous embodiments are described in particular in the dependent claims, each of which, taken by itself or in various combinations with each other, can represent an aspect of the invention.

A component according to the invention for a hot-dip coating system, which component comes into direct contact with an immersion bath containing molten metal during operation of the hot-dip coating system, comprises a metallic base body, wherein at least a portion of the surface of the base body is provided with a three-layer coating, which comprises a corrosion-resistant bonding layer arranged on the surface portion in question, a barrier layer arranged on the bonding layer, and a ceramic surface layer arranged on the barrier layer.

According to the invention, a special three-layer coating is arranged on the metallic base body of the component, wherein the properties of the individual layers of the coating are optimally adapted to the individual application. The metallic bonding layer arranged directly on the base body serves in particular to bond the metallic barrier layer permanently to the base body. As a result of the corrosion resistance, especially the oxidation resistance, of the bonding layer, furthermore, the base body is protected from corrosion and oxidation. The metallic barrier layer is a layer which is impermeable to chemicals, a property which also prevents chemicals from reaching the base body of the component. The ceramic surface layer is highly heat-resistant. The ceramic surface layer also prevents slag elements, for example, from adhering to or baking onto the component. As a result, the quality of the workpiece to be coated by the hot-dip coating system is improved, because no imprints or defects are transferred from the component to the workpiece guided by it. At the same time, the three-layer coating according to the invention increases the service life of the component in the immersion bath, which is associated with a positive cost effect with respect to maintenance, with a reduction of down times, and with an improvement of system availability. The base body can also be produced from a material which is less expensive than that of corresponding conventional components, because the three-layer coating according to the invention provides excellent protection of the base body from wear.

The component according to the invention can be used in immersion baths containing various metal melts. The metal melts can be, for example, melts of various zinc alloys with admixtures of, for example, aluminum, iron, magnesium, nickel, silicon, chromium, and/or rare earths. Alternatively, the metal melts can be melts of various aluminum alloys with admixtures such as iron, silicon, nickel, magnesium, tin, and/or chromium. As another alternative, the metal melts can be melts of various brass alloys, tin alloys, or copper alloys with appropriate admixtures.

The component according to the invention can be a product made from new raw materials. Alternatively, it can be fabricated by the processing of an existing component, in that this existing component is provided with the three-layer coating according to the invention.

According to an advantageous embodiment, the bonding layer is made at least partially from an iron, nickel, cobalt, or nickel-cobalt base alloy. In particular, the bonding layer can be made at least partially from a MCrAlY base alloy, wherein the base element M can be iron, nickel, or cobalt. The thickness of the bonding layer can be in the range of 20-300 μm, preferably in the range of 50-200 μm, and even more preferably in the range of 80-120 μm.

According to another advantageous embodiment, the barrier layer is made at least partially from a transition metal or an alloy of transition metals. In particular, the barrier layer can be produced at least partially from molybdenum, a molybdenum-containing alloy, or molybdenum carbide. The thickness of the barrier layer can be in the range of 100-500 μm, preferably in the range of 150-400 μm, and even more preferably in the range of 200-300 μm.

According to another advantageous embodiment, the surface layer is made at least partially from a pure oxide ceramic or an oxide ceramic provided with rare earths. In particular, the surface layer can be made at least partially from zirconium oxide to which yttrium has been added. The thickness of the surface layer can be in the range of 100-500 μm, preferably in the range of 150-400 μm, and even more preferably in the range of 200-250 μm.

According to another advantageous embodiment, the component is configured as a roller for guiding or deflecting a metal strip to be coated as it is being guided through an immersion bath. The component in this case is completely immersed in the bath.

According to another advantageous embodiment, the base body comprises a roller portion and two axial bearing journals, which are connected to the roller portion and arranged coaxially to it, wherein at least parts of the surfaces of each of the bearing journals are provided with the three-layer coating, and wherein a lateral surface of the roller body is provided with a metallic protective layer. The three-layer coating according to the invention acts to protect the bearing journals, as a result of which the wear in the unit consisting of the bearing journal and the bearing is considerably minimized for each bearing journal. The metallic protective layer can be made at least partially from molybdenum, a molybdenum-containing alloy, or molybdenum carbide.

According to another advantageous embodiment, the base body comprises a roller portion and two axial bearing journals, which are connected to the roller portion and arranged coaxially to it, wherein a metal bushing is installed on each bearing journal. As a result, the service life of the bearing journal is prolonged. The metal bushings can be made from carbon steels such as C45, C60, or C70; or from case-hardening steels/heat-treatable steels such as 42CrMo4. Metal bushings of this type are advantageous especially in conjunction with the use of the roller-shaped component in aluminum-containing melts. The metal bushings can be coated with the three-layer coating according to the invention In addition, the roller portion can also be coated with the three-layer coating of the invention. Alternatively, either the roller part or the metal bushings can be coated with the three-layer coating according to the invention.

A method according to the invention for producing a component, especially a guide or deflection roller, for a hot-dip coating system, which component comes into direct contact with an immersion bath containing liquid metal during operation of the hot-dip coating system, comprises the following steps:

-   -   providing a metallic base body;     -   applying a corrosion-resistant bonding layer to at least part of         the surface of the base body;     -   applying a barrier layer to the bonding layer; and     -   applying a ceramic surface layer to the barrier layer.

The advantages described above in reference to the component are associated correspondingly with the method. In particular, the component according to one of the above-described embodiments or according to any desired combination of at least two of these embodiments with each other can be produced by the use of the method according to the invention.

According to an advantageous embodiment, the bonding layer and the barrier layer are each applied by thermal or kinetic spraying. The bonding layer can be applied by spraying a feedstock containing iron, nickel, cobalt, or nickel-cobalt base alloy, especially a MCrAlY base alloy, the base element M of which is iron, nickel, or cobalt. In addition, the bonding layer can be applied to a thickness in the range of 20-300 μm, preferably of 50-200 μm, and especially preferably of 80-120 mum. The barrier layer can be applied by thermally or kinetically spraying a feedstock containing a transition metal, especially molybdenum, or an alloy of transition metals, especially a molybdenum-containing alloy or molybdenum carbide. In particular, the barrier layer can be applied in a thickness in the range of 100-500 μm, preferably in the range of 150-400 μm, and even more preferably in the range of 200-300 μm.

According to another advantageous embodiment, the surface layer is applied by thermal spraying. The surface layer can be applied by thermally spraying a feedstock containing a pure oxide ceramic or an oxide ceramic to which rare earths has been added, especially a zirconium oxide to which yttrium has been added. In particular, the surface layer can be applied to a thickness in the range of 100-500 μm, preferably in the range of 150-400 μm, even more preferably in the range of 200-250 μm.

According to another advantageous embodiment, the base body is provided with a roller portion and two axial bearing journals, which are connected to the roller portion and arranged coaxially to it, wherein at least parts of the surfaces of the two bearing journals are provided with the three-layer coating, and wherein a lateral surface of the roller body is provided with a metallic protective layer. This embodiment of the method is associated with the advantages described above with reference to the corresponding embodiment of the component. The metallic protective layer can be made at least partially from molybdenum, a molybdenum-containing alloy, or molybdenum carbide.

According to another advantageous embodiment, the base body is provided with a roller portion and two axial bearing journals, which are connected to the roller portion and arranged coaxially to it, wherein a metal bushing is installed on each of the bearing journals. The advantages described above with reference to the corresponding embodiment of the component are also associated correspondingly with this embodiment of the method.

In the following, the invention is explained in greater detail with reference to the attached figures, which illustrate preferred embodiments, wherein the features explained below can represent an aspect of the invention either alone or in various combinations with each other:

FIG. 1 shows a schematic diagram in the form of a longitudinal cross section of an exemplary embodiment of a component according to the invention in the form of a roller;

FIG. 2 shows a schematic diagram in the form of a longitudinal cross section of another exemplary embodiment of a component according to the invention in the form of a roller; and

FIG. 3 shows a schematic diagram in the form of a longitudinal cross section of another exemplary embodiment of a component according to the invention in the form of a roller.

FIG. 1 shows a schematic diagram in the form of a longitudinal cross section of an exemplary embodiment of a component 1 according to the invention for a hot-dip coating system (not shown), wherein the component 1 comes into direct contact with an immersion bath containing liquid metal during operation of the hot-dip coating system. The component 1 is configured as a roller for guiding or deflecting a metal strip to be coated as it is guided through the immersion bath.

The component 1 comprises a metallic base body 2, which has a roller portion 3 and two axial bearing journals 4, which are connected to the roller portion 3 and arranged coaxial to it. The roller portion 3 of the base body 2 is provided with a three-layer coating 5, which comprises a corrosion-resistant bonding layer 6, arranged directly on the surface of the roller portion 3; a barrier layer 7 arranged on the bonding layer 6; and a ceramic surface layer 8 arranged on the barrier layer 7. The bonding layer 6 is made at least partially from an iron, nickel, cobalt, or nickel-cobalt base alloy. The barrier layer 7 is made at least partially from a transition metal or an alloy of transition metals. The surface layer 8 is made at least partially from a pure oxide ceramic or an oxide ceramic provided with rare earths.

FIG. 2 shows a schematic diagram in the form of a longitudinal cross section of another exemplary embodiment of a component 10 according to the invention for a hot-dip coating system (not shown), wherein the component 10 comes into direct contact with an immersion bath containing liquid metal during operation of the hot-dip coating system. The component 10 is configured as a roller for guiding or deflecting a metal strip to be coated as it is guided through the immersion bath.

The component 10 comprises a metallic base body 12, which has a roller portion 13 and two axial bearing journals 14, which are connected to the roller portion 13 and arranged axially to it. The surfaces of each of the bearing journals 14 are provided with the three-layer coating 5, which comprises a corrosion-resistant bonding layer arranged directly on the surface of the roller portion 13, a barrier layer arranged on the bonding layer 6; and a ceramic surface layer 8 arranged on the barrier layer 7. The bonding layer is made at least partially from an iron, nickel, cobalt, or nickel-cobalt base alloy. The barrier layer 7 is made at least partially from a transition metal or an alloy of transition metals. The surface layer 8 is made at least partially from a pure oxide ceramic or an oxide ceramic provided with rare earths. The lateral surface of the roller part 13 is provided with a metallic protective layer 11, which is made at least partially from molybdenum, a molybdenum-containing alloy, or molybdenum carbide.

FIG. 3 shows a schematic diagram in the form of a longitudinal cross section of another exemplary embodiment of a component 20 according to the invention for a hot-dip coating system, wherein the component 20 comes into direct contact with an immersion bath containing liquid metal during operation of the hot-dip coating system. The component 20 is configured as a roller for guiding or deflecting a metal strip to be coated as it is being guided through the immersion bath.

The component 20 differs from the exemplary embodiment shown in FIG. 1 in that a metal bushing 21 is installed on each of the bearing journals 4. The metal bushings can be made of carbon steels such as C45, C60, or C70, or of case-hardening/heat-treatable steels such as 42CrMo4. To avoid repetition, reference can be made here to the description of FIG. 1 given above.

LIST OF REFERENCE NUMBERS

-   1 component -   2 base body -   3 roller portion -   4 bearing journal -   5 three-layer coating -   6 bonding layer -   7 barrier layer -   8 surface layer -   10 component -   11 metallic protective layer -   12 base body -   13 roller portion -   14 bearing journal -   15 component -   21 metal bushing 

1-12. (canceled)
 13. A component for a hot-dip coating system, which component comes into direct contact with an immersion bath containing liquid metal during operation of the hot-dip coating system, comprising: a metallic base body; and a three-layer coating on at least a portion of a surface of the base body, the three-layer coating comprising a corrosion-resistant bonding layer arranged directly on the surface of the portion in question, the bonding layer being made at least partially from an iron, nickel, cobalt, or nickel-cobalt base alloy, a barrier layer arranged on the bonding layer, the barrier layer being made at least partially from molybdenum, a molybdenum containing alloy, or molybdenum carbide, and a ceramic surface layer arranged on the barrier layer, the surface layer being made at least partially from an oxide ceramic containing rare earths.
 14. The component according to claim 13, wherein the component is a roller for guiding or deflecting a metal strip to be coated as the metal strip is being guided through the immersion bath.
 15. The component according to claim 14, wherein the base body comprises a roller portion and two axial bearing journals connected to the roller portion and arranged coaxially to the roller portion, wherein at least parts of surfaces of each of the bearing journals are provided with the three-layer coating, and wherein a lateral surface of the roller portion is provided with a metallic protective layer.
 16. The component according to claim 14, wherein the base body comprises a roller portion and two axial bearing journals connected to the roller portion and arranged coaxially to the roller portion, wherein a metal bushing is installed on each of the bearing journals.
 17. A method for producing a component for a hot-dip coating system, which component comes into direct contact with an immersion bath containing liquid metal during operation of the hot-dip coating system, the method comprising the steps of: providing a metallic base body; applying a corrosion-resistant bonding layer made at least partially from an iron, nickel, cobalt, or nickel-cobalt base alloy to at least part of a surface of the base body; applying a barrier layer made at least partially from molybdenum, a molybdenum containing alloy, or molybdenum carbide to the bonding layer; and applying a ceramic surface layer made at least partially from an oxide ceramic containing rare earths to the barrier layer, the layers forming a three-layer coating.
 18. The method according to claim 17, wherein the bonding layer and the barrier layer are each applied by thermal or kinetic spraying.
 19. The method according to claim 17, wherein the surface layer is applied by thermal spraying.
 20. The method according to claim 17, wherein the base body has a roller portion and two axial bearing journals connected to the roller portion and arranged coaxially to the roller portion, the three-layer coating being applied to at least parts of surfaces of each of the bearing journals, the method further including applying a metallic protective layer to a lateral surface of the roller section.
 21. The method according to claim 17, wherein the base body has a roller portion and two axial bearing journals connected to the roller portion and arranged coaxially to the roller portion, the method further including installing a metal bushing on each of the bearing journals. 